The respective roles of nucleus and cityoplasm in early mammalian development are little understood. What effect maternally inherited cytoplasmic components have on differentiation, and the developmental stage to which they persist are largely unknown. We propose to investigate nuclear/cytoplasmic interactions in the mouse embryo using a novel nuclear tranplantation technique. This technique will be employed to determine the ability of nuclear transplant empryos to undergo normal development and also define the developmental stage at which nuclear endoced gene products can first be detected. Possible maternally derived cytoplasmic contributions to the embryonic phenotype will also be investigated. Experiments regarding the latter were specifically chosen to define possible cytoplasmic effects at different stages of development (ranging from early preimplantation development to late gestational embryogenesis). It is hoped that these experiments will delineate the nuclear/cytoplasmic origin of embryonic gene products and events in addition to increasing our understanding of the biology of nuclear transplantation in mammals.